Angiotensin (AII) has been shown to stimulate jejunal sodium (Na+) and water transport in vivo. However, the mechanism of action and physiological role of the intestinal effects of the hormone are unclear. Therefore, this study will show that the increase in jejunal Na+ and water absorption following extracellular fluid (ECF) reduction is mediated by the renin angiotensin system, demonstrate that ECF depletion results in increased jejunal Na+ and water absorption which is independent of changes in intracellular fluid (ICF) volume, define the site of action of AII within the sympathetic nervous system (SNS) leading to increased Na+ and water absorption and determine the intestinal cell types that have specific yield-adrenergic binding sites and receptors for AII. Three general protocols will be employed to accomplish these aims. First, jejunal electrolyte and water absorption will be measured from closed intestinal sacs in anesthetized rats following non-hypotensive hemorrhage, water deprivaton and Na+ depletion. All are models of ECF delpetion but either have no effect or decrease and increase the ICF respectively. Plasma aldosterone, AII and ECF volume will be determined in these animals. Jejunal absorption also will be determined following adrenalectomy, nephrectomy and after treatment with spironolactone, captopril and a specific renin inhibitor in ECF-depleted rats. The site of interaction of AII within the SNS will be determined by circulating blood containing AII through the vascularly isolated head or mesenteric circulationof a recipient animal, while simultaneously measuring jejunal absorption from closed sacs in the recipient. To determine the intestinal cell types having yield and AII receptors, both light and electronmicroscopy autoradiography for I25I AII and 3H-prazosin will be performed in combination with flouresence microscopy for catecholamines and immunohistochemistry for DBetaH. The long term objectives of this study are to increase understanding of the normal physiological control of intestinal absorption by hormones and the SNS.